1. Field of the Invention
The invention relates to de-icers for aircraft and, more particularly, to de-icers that operate by deforming ice-accumulating surfaces.
2. Description of the Prior Art
The accumulation of ice on aircraft wings and other aircraft structures in flight is a danger that is well known. As used herein, the term "structural members" is intended to refer to any aircraft surface susceptible to icing during flight, including wings, stabilizers, engine inlets, rotors and so forth. Attempts have been made since the earliest days of flight to overcome the problem of ice accumulation. While a variety of techniques have been proposed for removing ice from aircraft during flight, these techniques have had various drawbacks that have stimulated continued research activities.
One approach that has been used extensively is so-called mechanical de-icing. In mechanical de-icing, an ice accumulating surface is distorted in some manner so as to crack ice that has accumulated thereon for dispersal into the airstream. A popular mechanical deicing technique is the use of expandable tube-like structures that are periodically inflatable. The tube-like structures are mounted on the outer surface of the structural member. Inflation of the structures results in their expansion or stretching by 40% or more. Such expansion typically occurs over approximately 2-6 seconds and results in a substantial change in the profile of the de-icer, thereby cracking accumulated ice. Unfortunately, expansion of the devices can negatively influence the airflow passing over the aircraft structure. Also, they are most effective when ice has accumulated to a substantial extent, approximately 0.25 inch or more, thereby limiting their effectiveness. Desirably, ice removal would be accomplished long before accumulations approximating 0.25 inch have accumulated.
De-icers adapted to be attached to an outer surface of a structural member are disclosed in U.S. Pat. No. 4,690,353 to Haslim et al. and U.S. Pat. No. 4,875,644 to Adams et al. In the '353 patent, for example, one or more overlapped flexible ribbon conductors are imbedded in an elastomeric material that is affixed to the outer surface of a structural member. The conductors are fed large current pulses from a power storage unit. The resulting interacting magnetic fields produce an electro-expulsive force that distends the elastomeric member to remove thin layers of ice.
Another mechanical de-icing technique utilizes internal "hammers" to distort the leading edges of aircraft structures. Such an approach is disclosed in U.S. Pat. No. 3,549,964 to Levin et al., wherein electrical pulses from a pulse generator are routed to a coil of a spark-gap pressure transducer disposed adjacent the inner wall of the structural member. The primary current in the coil induces an eddy current in the wall of the structural member and the magnetic fields produced by the currents interact so as to deform the member.
U.S. Pat. Nos. 3,672,610 and 3,779,488 to Levin et al. and U.S. Pat. No. 4,399,967 to Sandorff disclose aircraft de-icers that utilize energized induction coils to vibrate or torque the surface on which ice forms. Each of these devices employs electromagnetic coils or magneto-restrictive vibrators located on the side of the surface opposite to that on which ice accumulates. In U.S. Pat. No. 3,809,341 to Levin et al., flat buses are arranged opposite one another, with one side of each bus being disposed adjacent an inner surface of an ice-collecting wall. An electric current is passed through each bus and the resulting interacting magnetic fields force the buses apart and deform the ice-collecting walls.
Each of the de-icers disclosed by Levin et al. and Sandorff are mounted on a support element, such as a spar associated with the structural member. The special arrangements of conductors, spacers, stringers and/or supports used to mount these de-icers tend to result in undue manufacturing costs, add unwanted weight and render economical and efficient manufacturing procedures difficult to attain.
U.S. Pat. No. 4,678,144 to Goehner et al. is directed toward an electro-impulse de-icing system for an aircraft in which an inductor coil is mounted to an inner surface of an airfoil. As disclosed by Goehner et al., each de-icer includes a ribbon coil spaced from the inner surface of the airfoil by doubler sheets of aluminum. The coil is conformed to the shape of the airfoil surface through use of a block held in place by a support assembly, the support assembly includes a foam layer sandwiched between two layers of fiberglass. The sandwiched foam layer is secured by two brackets, each of which is mounted to the inner surface of the airfoil.
The Goehner et al. mounting arrangement represents an advancement over the above-discussed arrangements of Levin et al. and Sandorff. In contrast to the Levin et al. and Sandorff arrangements, the Goehner et al. coil need not be mounted to a structural support element of the structural member and the coil can be mounted relatively near the inner surface of the structural member. It is believed, nonetheless, that the Goehner et al. mounting arrangement possesses a number of distinct disadvantages.
In particular, the Goehner et al. mounting arrangement is neither convenient nor economical to install since a relatively large group of components must be assembled in order to mount the coil along the inner surface of the airfoil. Moreover, a significant number of these components, such as the coil conforming block, would be unnecessary in a more efficiently designed de-icer.
U.S. Pat. No. 4,253,704 issued to I. A. Levin discloses a method and apparatus for disintegrating a material. A coil is supported by an arm which is attached to a wall by an assembly of angle brackets. A plurality of such assemblies may be distributed along the wall. The individual coil devices are cycled in order to initiate a deflection in the wall which crushes frozen or caked material adjacent the wall. Though simpler in construction than the Goehner device, this mounting arrangement is more complicated than that contemplated by the present invention.
Despite advances taught by the prior art, particularly those advances associated with attachable external de-icers disclosed by U.S. Pat. No. 4,875,644 to Adams et al. and U.S. Pat. No. 4,690,353 to Haslim et al., many installers of de-icers desire de-icing systems in which the coil or conductive layers can be mounted along the inner surface of the structural member. As discussed above, however, many of the prior art systems adapted to be secured along the inner surface of the structural member are neither economical nor convenient to install. It is believed that known de-icing arrangements adapted to be mounted along the inner surface of the structural member fail to appreciate the need for a mounting arrangement that is relatively compact, lightweight and easy to install.